Loading in 5 sec....

Longitudinal Spin at RHICPowerPoint Presentation

Longitudinal Spin at RHIC

- By
**lel** - Follow User

- 156 Views
- Uploaded on

Download Presentation
## PowerPoint Slideshow about ' Longitudinal Spin at RHIC' - lel

**An Image/Link below is provided (as is) to download presentation**

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript

### Longitudinal Spin at RHIC

Cameron McKinney

29th Winter Workshop on Nuclear Dynamics

February 7, 2013

Introduction: Longitudinal Spin at RHIC

From the RHIC Spin white paper (2012):

Helicityparton density functions (PDFs) carry vital information on the extent to which quarks and gluons with a given momentum fraction x have their spins aligned with the spin direction of a fast moving nucleon in a helicityeigenstate. The corresponding integrals over all x relate to one of the most fundamental, but not yet satisfactorily answered questions in hadronic physics: how is the spin of the proton distributed among its constituents?

Proton Momentum

Proton Spin

Helicity

∆q(x,Q2)

∆g(x,Q2)

, where superscript +(-)

indicates parton spin aligned (anti-aligned) with proton spin

Cameron McKinney

Introduction: Longitudinal Spin at RHIC

Where does the proton’s spin of ½ come from?

}

RHIC longitudinal spin aims: ΔG and sea quark contribution to ΔΣ

Cameron McKinney

Outline

- ΔG at RHIC
- Accessing ΔG with double longitudinal spin asymmetries, ALL
- Measuring ALL at RHIC
- ΔG from ALL: Global analysis (by DSSV) with RHIC data
- Impact of recent results from PHENIX+STAR
- Next steps

- Sea quark polarization at RHIC: the W program
- Physics motivation: sea-quark polarization from ALW
- Recent ALW results from STAR and PHENIX
- Contribution of current and future data to DSSV global analysis

3

Cameron McKinney

Probing Helicity Structure in Polarized pp Collisions

Factorization: can break down cross section into pQCD-calculable hard scattering and pQCD-incalculable PDFs and fragmentation functions

pp hX

Double longitudinal spin asymmetry is sensitive to Δgand Δq

4

Cameron McKinney

Measuring ALL at RHIC

- ALLis measured by determining difference in particle yields between ++ and +- crossings (with an additional factor to normalize luminosities for crossing types)
- Bunch spinpatterns include ++,+-, -+, and -- crossings in each fill

- N is the yield of the final state measured
- e.g. jets, di-hadron or di-jet states

Cameron McKinney

10

Measuring ALL at RHIC: ALLfor Inclusive Jets at STARSTAR Run 6 inclusive jet

Mid-rapidity, s=200 GeV

PRD 86, 032006 (2012)

Process Fraction

pT [GeV]

- STAR inclusive jet measurements at mid-rapidity have most statistics where qg processes dominatesensitive to sign of Δg

Good discriminative power between calculations with different assumptions for G

6

Cameron McKinney

Measuring ALL at RHIC: ALLfor Inclusive 0at PHENIX

PHENIX Run5+6 √s = 200 GeV: PRL103, 012003

Process Fraction

- PHENIX ALL for inclusive π0 covers a scaled-down pT range compared to STAR—π0’s carry a fraction of jet momentum
- Smallest statistical uncertainty where process fraction for gg ≈ qgweaker constraint on negative Δg, better constraints on positive Δg

7

Cameron McKinney

ΔG from ALL: QCD Global Analysis

- DSSV (de Florian, Sassot, Stratmann, Vogelsang): global NLO analysis including polarized data from inclusive DIS, SIDIS, and RHIC pp collisions
- Phys.Rev.Lett.101:072001, 2008 and Phys.Rev.D80:034030,2009.

Inclusive DIS data: routinely used for PDF fits

Semi-inclusive DIS data: previously used only in DNS fit

flavor separation

First RHIC polarized pp data: first fit by DSSV

467 data points in total (10% from RHIC)

Cameron McKinney

ΔG from ALL: QCD Global Analysis

- Methodology Overview:
- Parameterize distributions for quarks and gluons
- Impose additional physics-based constraints (e.g. )
- Evolve distributions from the input scale to the various Q2 of experimental data
- Find corresponding observables as a function of kinematic variable (pTfor pp, x for DIS)
- Minimize of fit of calculated observables to data

Cameron McKinney

ΔG from ALL: QCD Global Analysis

- Methodology Overview:

Parameterize distributions…

…calculate observables and fit to data

(STAR and PHENIX Run 5 + Run 6 data shown).

DSSV: Phys.Rev.Lett.101:072001, 2008

Cameron McKinney

ΔG from ALL: DSSV Results

Well-determined by DIS

Main constraints to sea quarks from SIDIS (and DIS for strange quark)

Best constraints for ΔG now provided by RHIC

de Florian, Sassot, Stratmann, Vogelsang

Phys.Rev.D80:034030,2009

Cameron McKinney

ΔG from ALL: Run 9 ALL Measurements at RHIC

STAR preliminary

- Substantially larger figure of merit (P4L) from Run 9 than in all previous runs combined.

Cameron McKinney

ΔG from ALL: DSSV with Run 9 Data

- DSSV++ is a new, preliminary global analysis from the DSSV group that includes 2009 ALL measurements from PHENIX and STAR
- First experimental evidence of non-zero gluon polarization in the RHIC range (0.05 < x< 0.2)!

Cameron McKinney

ΔG from ALL: DSSV with Run 9 Data

Cameron McKinney

ΔG at RHIC: Next Steps

- Large uncertainty still remains in both the shape of Δg(x) and its integral, particularly for small x region not yet accessed by RHIC data

- RHIC will continue to improve constraints through the following:
- Reduced statistical and systematic uncertainties for all ALL channels
- Better handle on measured x through correlation measurements
- Access lower x region through forward measurements and

Cameron McKinney

ΔG at RHIC: Next Steps: Correlation Measurements

Measure two jets or jet tags to constrain event kinematics; provides data on shape of

STAR di-jet projections;

one jet at forward rapidity (1<<2) to push down x2

ALL for back-to-back ’s at mid-rapidity—more data needed!

Cameron McKinney

ΔG at RHIC: Next Steps: Low x with the MPC in PHENIX

Larger smaller x2

MPC: 3.1<<3.9

Projections of cluster ALLwith Run 13 for 2009 DSSV best fitand Δg upper uncertainty band

First PHENIX forward measurement of ALL for merged EM clusters (~80% 0)

Cameron McKinney

ΔG at RHIC: Next Next Steps: Electron-Ion Collider

- Proposed electron-ion collider could greatly enhance our knowledge of Δ𝑮 beyond current capabilities of RHIC
- Polarization of both electron (~80%) and proton beam (70%)
- Very high luminosity (~10 fb-1 used for projection below achievable in 1-2 months of running)
- Broad coverage in Q2 and x allows precise determination of Δg(x) through scaling violation

-DSSV+

-w proj. EIC data

(~10 fb-1)

x

Cameron McKinney

Sea Quark Polarization: W Program at RHIC

Previously constrained by SIDIS:

Large uncertainties from fragmentation functions and lack of data

- Measurement of parity-violating W production at RHIC complements SIDIS data
- Leptonic final stateno FF dependence
- Large Q2 ~ MW2
- W couples only to left-handed quarks and right-handed anti-quarksfixes quark helicity and flavor

Cameron McKinney

W Program at RHIC: Forward Upgrades

- Selecting kinematic ranges allows sensitivity to specific quark/anti-quark helicities; upgrades allow lepton measurements at forward rapidity

Forward Gem Tracker

- Central (barrel) region (We , ||<1)
- First data from 2009: PRL106, 062002 (2011)

- Forward (endcap) region (We , 1<||<2) :
- Forward tracker upgrade, first data in 2012

- Central Arms (We , ||<0.35)
- First data from 2009: PRL106, 062001 (2011)

- Forward Arms (W , 1.2<||<2.4) :
- Trigger upgraded, first data from 2011

RPC-1 North and RPC-3 North

20

Cameron McKinney

W Program at RHIC: Forward Measurements of AL

- First measurement of by PHENIX in 2011 (

(towards )

Cameron McKinney

W Program at RHIC: Forward Measurements of AL

- STAR preliminary AL for Run 12 already has sizeable effect on DSSV fits

DSSV++ (includes STAR Run 12)

DSSV+

(DSSV with COMPASS)

Cameron McKinney

W Program at RHIC: Next Steps

- Run 13 goal: finish W program by reaching total

Projections including expected data in 2013

Cameron McKinney

Summary

- The PHENIX and STAR collaborations are making important contributions to our understanding of the helicity structure of the nucleon
- ALL measurements provide best constraints to ΔG for QCD analyses
- For the first time we see evidence of a non-zero gluon polarization
- Large dataset from Run 13 at of 510 GeVwill lead to precise measurement of at 0.05 < x < 0.2
- ALL for correlations and at forward rapidity will reduce uncertainties in the shape and integral of Δg(x) while broadening the coverage in x down to ~10-3

- W program at RHIC will lead to substantial improvement in the understanding of the sea quark polarization in the near term with the expected statistics from Run 13
- The STAR AL from Run 12 has already provided DSSV with a stronger constraint on the sea quark polarization

Cameron McKinney

Cameron McKinney

Constraining x/probing low x

Fwd–Rapidity 3.1<|η| < 3.9, 500 GeV

Single

π0

Effect of higher COM energy

Di-π0

Cameron McKinney

Central region: W e from Run9

ALe+/e-

ALe+/e-

e+

e-

e-

e+

PHENIX: PRL106, 062001 (2011)

STAR: PRL106, 062002 (2011)

P=0.39 L=8.6/12 pb-1 in PHENIX/STAR

27

Cameron McKinney

Download Presentation

Connecting to Server..